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Dale Luthringer was hiking last month through a stand of 500-year-old hemlocks in the Allegheny National Forest when he made a discovery he never wanted to make.

In fading light near the end of the day, he kicked over a hemlock branch lying on the ground. On the underside of a sprig of green needles was a white, waxy mass.

Inside that small ball were the eggs of the hemlock woolly adelgid. The tiny Asian invader was in the big trees of the state's only national forest.

"I only found the single egg mass, but the infestation is likely much greater in what is definitely one of the most ecologically significant areas of old-growth hemlock in the state if not the Northeast," Mr. Luthringer said after the state Department of Agriculture confirmed the find earlier this week.

"Finding the adelgid in the national forest's old-growth was like a death in the family," said Mr. Luthringer, an environmental education specialist who works in nearby Cook Forest State Park for the state Department of Conservation and Natural Resources. "There's grief, but you know it's real and you have to deal with it."

The hemlock woolly adelgid's arrival in the old-growth hemlocks of the national forest's Tionesta Research Natural Area comes after its decades-long march through the forests of the southern and middle Appalachians. It heralds a grim future for Pennsylvania's state tree.

Tens of thousands of the evergreens, many of them more than 400 years old, could die over the next five to 10 years, said Andrea Hille, a national forest silviculturist.

The adelgid already has wiped out old-growth hemlocks in the Great Smoky Mountains National Park and 95 percent of the hemlocks in Shenandoah National Park in Virginia.

"This finding is important because of the uniqueness of the old growth," Ms. Hille said.

According to the Forest Service, the sap-sucking insects were accidentally brought into the U.S. in the 1950s, most likely in a shipment of plants from Asia. They don't fly, but the sticky egg sacks hitchhike on humans, animals and especially birds from tree to tree, where they hatch and feed on the sap in young branches.

They overwinter on the underside of the flat hemlock needles, laying eggs and secreting a white, waxy covering that looks like a tiny tuft of wool, hence the name.

Eastern hemlocks make up 5 percent to 10 percent of the forest throughout the Appalachians, but Ms. Hille said they make up 42 percent of the trees in the 4,000-acre research area, which contains about 12 percent of all the original forest left in the state. Beech trees in the research area also are dying due to beech bark disease.

Ms. Hille said the old growth hemlocks have trunk diameters of 40 inches or more and stand up to 125 feet tall. Mr. Luthringer discovered the adegid egg mass under old-growth hemlocks in the West Fork area.

It wasn't the first sighting of the adelgid in the national forest, but it's the first time the bugs have been found in the forest's old growth hemlocks. This spring the adelgid was identified in a young hemlock stand along the Allegheny River below the Kinzua Dam, along the Clarion River, and in Cook Forest and Clear Creek state parks. They have now been found in 62 of the state's 67 counties.

Hemlocks can grow up to 175 feet tall and live up to 900 years. They fill an important ecological niche, cooling streams, providing wildlife cover, and enhancing forest aesthetics and recreational values, according to the Forest Service.

To combat the invasive pest and save as many trees as possible, the Forest Service is partnering with the Pennsylvania Department of Conservation and Natural Resources and Game Commission, The Nature Conservancy, and several New York State natural resource agencies to develop a "hemlock conservation strategy" for the High Allegheny Plateau region of northwestern Pennsylvania.

Options for treating the infestation, including pesticides and the introduction of beetles that feed on the adelgid, are limited because of the size of the research area, the number of hemlocks, and the cost, said Rick Turcotte, a Forest Service entomologist in Morgantown, W.Va.

"As soon as we get a break in the weather, we will survey the area and figure out how big it is," Mr. Turcotte said. "Then I'll make recommendations about how to treat it."

Mr. Luthringer said the state treated 1,390 hemlocks in Cook Forest State Park this summer, spending $13,000 on beetle releases and pesticide, a cost that doesn't include staff pay or equipment.

"We've got to treat the national forest hemlocks as soon as we can. The longer we wait the more widespread and expensive it will get," Mr. Luthringer said. "We have to think of the resource first. We're probably going to lose a lot of hemlock, but if we don't do anything, we'll lose them all."

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